But he insisted that operations overseas - including successful seizures at sea by the Royal Navy - are starting to have an impact.

He claimed cocaine wholesale prices are £5,000 greater in the UK than in the Netherlands, pointing to a radical reduction in the supply of the drug.

However, he did admit that this had made little difference to street prices and that, increasingly, the drug was being diluted or "cut" with other substances before being sold cheaply on the streets.

During the session, Labour MP David Winnick asked him: "There doesn't seem to be the slightest indication that organised crime in this country is being undermined.

"Master criminals are not going in fear of their lives because of your organisation. Why should the British public consider that you have made the slightest difference?" But Sir Stephen insisted the pay-off from SOCA's new approach would come "in two or three years' time", adding: "We've been going 21 months.

"This is a marathon, not a sprint. We need some time and space to get on with it."

Last night, Home Office immigration minister Liam Byrne said no final decision had been made over whether to force South African visitors to apply for visas.